The invention relates to a method of driving a display device comprising an electro-optical display medium between two supporting plates, a system of picture elements arranged in rows and columns with each picture element being constituted by picture electrodes provided on the facing surfaces of the supporting plates, and a system of row and column electrodes, the method including selecting a row of picture elements via the row electrodes by means of non-linear switching elements arranged in series with the picture elements, and presenting a data signal via the column electrodes.
The invention also relates to a display device in which such a method can be used.
In this respect it is to be noted that the terms "row electrode" and "column electrode" in this Application may be interchanged if desired, so that references to a column electrode and a row electrode may be taken to mean a row electrode, and a column electrode respectively.
A display device of this type is suitable for displaying alpha-numeric and video information with the aid of passive electro-optical display media such as liquid crystals, electrophoretic suspensions and electrochromic materials.
A display device as mentioned above in which back-to-back diodes are used as switching elements is known from U.S. Pat. No. 4,223,308. A memory function is obtained by using switching elements so that the information presented to a driven row remains present to a sufficient extent across a picture element during the time when the other row electrodes are driven. However, due to capacitive crosstalk owing to the capacitance of the non-linear switching elements this information may have a varying value because the same columns are used for presenting data signals upon selection of different rows of picture elements.
The voltage across a picture element may then change in such a manner that the transmission level (grey level) becomes higher or lower than the intended value. If the grey levels are to be fixed exclusively via the transmission curve, the number of grey levels is limited to a large extent by the crosstalk in relation to the maximum signal level.
The crosstalk due to signal changes is dependent in the first instance on the capacitance of the non-linear switching elements.
Another possibility of realizing grey levels is to divide a picture element into a number of sub-segments in which the fraction of the number of selected sub-segments determines the grey level. This requires an extra drive with extra column electrodes.
Such a division without extra drive may also be used for the purpose of providing a given redundancy because connections may drop out. This division usually leads to smaller sub-elements for which smaller picture electrodes are used. However, this results in the capacitance of the picture elements decreasing (relatively) with respect to that of the non-linear switching elements. Consequently the crosstalk increases.